For economical and environmental reasons, water based paints are increasingly used in industrial production applications. For high transfer efficiency, the coatings are often applied by means of electrostatic spray guns. Water based paints present problems with electrostatic applicators due to their electrical conductivity. In manufacturing production lines, it is sometimes desirable to have an electrically isolating paint color change system for selectively supplying different color electrically conductive paints to an electrostatic applicator. In early color change systems of this type, the entire paint delivery system from the supply tanks for the different color paints to the spray gun was electrically isolated from ground. In other systems, only the colored paint currently supplied to the spray gun was isolated from ground. This arrangement was not very acceptable because of the large mass which had to be maintained at the high voltage. The capacitance of the large mass stored a large amount of electrical energy which could produce a high energy discharge if a grounded object was brought near the spray gun. Also, there was a risk to personnel in the area because of the large system which typically was charged from 50,000 volts to over 100,000 volts.
Another approach was to provide an electrically isolated reservoir which held a charge of the paint currently be applied. Either the reservoir was filled while the high voltage was interrupted or a voltage block was provided between the supply tanks and the isolated reservoir. This was accomplished, for example, by dripping the paint into the reservoir to interrupt the electrical path through the paint supply tank to ground. Neither of these arrangements permitted rapid color change.